APPLICATION OF MANURES G5 



genous manures applied to crops, and continued for 

 several years, gives the relative value of nitrogen 

 various forms as follows : — 



Nitrate of sodium , , . , , lOO 



Sulphate of ammonium 90 



Blood, powdered horn, green crops 70 



Steamed bone dust, fish manure, meat guano . . . . 60 



Farmyard manure 45 



Wool dust 30 



Powdered leather 20 



Working in the same way, Wagner found that 

 taking the effect of phosphoric acid in superphosphate 

 as 100, its effect in Thomas' slag was 58, and in 

 Peruvian guano 30, during the first year of their 

 application. Such average figures give a correct general 

 idea of the relative values of manures ; but the values 

 will in fact vary considerably with different soils and 

 seasons. 



Taking the market prices of manures, it is possible 

 in many cases to calculate the cost per lb. of their 

 constituents. A common phrase in the manure trade 

 is ''price per unit.'' When the units in a percentage 

 analysis are multiplied by this price we obtain the 

 value per ton. Thus, if nitrate of sodium containing 

 15'6 per cent, of nitrogen is worth £9 a ton, the value 

 of nitrogen per unit is lis. 6d. Again, if a mineral 

 superphosphate is worth £2 15s. a ton, and contains 

 67 per cent, of gypsum worth ^£1 5s. per ton, and 

 12 per cent, of soluble phosphoric acid, the unit value 

 of the phosphoric acid is 3s. 2d. If we regard the 

 gypsum as of no value, the price per unit of the 

 phosphoric acid becomes 4s. 7d. 



Application of Manures.— A manure can be efficacious 

 only when its constituents are brought into contact 



